Know Your 3D Filament - TPU
What is TPU?
TPU material is a group of thermoplastic elastomers with good elasticity and resistance to stresses like abrasion and oil lubricants. Its structure consists of soft and hard segments linked together in the chain. Thermoplastic Polyurethane or TPU is referred to as the bridge between rubbers and plastics. The material appears rubber-like, which means it can be extremely flexible, durable and smooth to the touch. All these properties and compound versatility makes TPU widely used in many industries for coatings, components and consumer goods. Of the many kinds of flexible 3D printer filaments, TPU is slightly more rigid, making it easier to extrude and use. It is a medium-strength material with very high flexibility and durability, able to withstand much higher compressive and tensile forces than its more common counterpart’s PLA and ABS.
Advantages of TPU Flexible Filament
TPU material has a number of features, making it a great choice for a wide range of uses. It is resistant to abrasion, oil, chemical and wearing, which makes it perfect for use in industries such as the automotive industry. TPU printed parts are also resistant to low temperatures, which means that it does not become brittle and difficult to work with.
Compared to TPE, which is also a flexible filament, TPU is a bit easier to print and retains its elastic properties better at lower temperatures. TPU material also has a higher abrasion resistance and a higher resistance to oils and greases.
TPU filament, unlike other stiffer thermoplastic, has qualities that include flexibility and conformity. It also has an excellent interlayer adhesion and no curling or delamination during the 3D printing process, when using the right settings.
TPU is commonly used in caster wheels, automotive instrument panels, sporting goods, power tools, medical devices, footwear, drive belts, inflatable rafts, and a number of extruded film and sheet applications. TPU is also a good material to be used in the outer cases of mobile devices such as tablets and phones.
Printing Tips & Tricks
The recommended extrusion temperature range is between 225-250°C depending on the type of a 3D printer and a TPU filament you have. However, keep in mind that printing with higher temperatures will allow the filament to melt faster and to flow easier from a nozzle.
Optimize the feed rate:
It is best to use slow consistent feed for printing flexible material. It is a fact that the if the material is elastic and can become uncontrollable if there are any sudden changes to the speed of the print. Increased print speeds can result in a compression of the filament, which can lead to a jam. It takes a number of attempts to determine the optimal printing speed, but it is good to start with the speed of 15 to 20 mm/s.
To achieve this using TPU material, print at lower layer heights, ensuring they are in the range of 0.1mm to 0.2mm. At the lower layer height, there is a requirement for less plastic and that means that the extruder feeds at a lower rate which eases the burden on the filament.
Optimize the retraction settings
Because TPU material is flexible and elastic, it makes it very sensitive to fast movements such as retractions. Therefore, to successful 3D print using the TPU filament, it is crucial that you optimize the retraction settings to limit the movements. It’s crucial, to begin with, a small retraction at a slower speed to avoid any possible oozing from the extruder (hot-end).
Use Direct Drive Extruders
The general opinion is in favor of 3D printing flexible materials with a Direct Drive extruder. You can also achieve the same results when using the right settings on a 3D printer with Bowden extruder. It is important for the path in which the filament travels to the melt zone to have tight tolerances, which can prevent any coiling.
Placement of Spool
When it comes to printing with flexible material, even a small tweak to the spool material makes a large difference. Commonly the extruder drive wheel pulls the filament into the extruder, resulting in a small unwinding of plastic from the spool. In the case of TPU, since it is elastic, the filament is pulled and stretched resulting in under extrusion. Therefore, mount the spool above the printer which can unwind downwards resulting in less elongation.
Use a negative tolerance and avoid using rafts
When you are designing a part that is flexible and will be used as a mating part with another part, it is worth considering negative tolerance between the parts. This will allow the flexible part has the ability to stretch over the other part (the matching of the parts will be good).
Avoid using rafts while printing with TPU because the base layer has a higher rate of extrusion which could lead to a problem.
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